1. Field of the Invention
The present invention relates to determining cardiac output of a patient, and more particularly, to determining the cardiac output of a patient through an extracorporeal cardiopulmonary support circuit, wherein flow through at least a portion of the extracorporeal cardiopulmonary support circuit is reversed and a measurement at the reversed flow is taken from which the cardiac output is determined.
2. Description of Related Art
Respiratory failure requiring pulmonary support affects in excess of 300,000 people in the United States per year. Approximately one-half of these patients suffer from adult respiratory distress syndrome (ARDS). Adult respiratory distress syndrome is an acute inflammatory lung disease with a mortality rate of 50%. This disease is characterized by increased capillary permeability resulting from the development of interstitial edema and alveolar flooding. For the vast majority of patients with ARDS, there is no specific treatment, or supportive therapy. Supportive therapy for ARDS focuses on mechanical ventilation. An alternative life support modality, such as extracorporeal oxygenation, can be a therapeutic option for acute respiratory failure in both infants and adults.
In addition, extracorporeal circulation (perfusion) is used for the most part in cardiac bypass surgery. In a total bypass, all the systemic venous return blood of the patient is diverted from entering the right side of the heart and into an extracorporeal circuit. In such application, the extracorporeal circuit includes a heart-lung machine that comprises a pumping function and an oxygenation function, completely taking over cardiopulmonary function for the patient, returning oxygenated blood to the aorta, downstream of the cardiopulmonary circuit. In a partial bypass only a portion of the blood is diverted to the extracorporeal circuit, the remaining flow passing to the heart, the lungs and from the lungs through heart to the systemic circulation.
A use of extracorporeal circulation as “extracorporeal life support” can include “extracorporeal membrane oxygenation” known by the respective acronyms of “ECLS” or “ECMO”, for simplicity herein called ECMO. As opposed to the more conventional extracorporeal circulation and substitution or assist of the cardiac function, ECMO connotes the application of such support to supply oxygenation where the native lungs may be compromised. This is especially useful for neonates, including premature birth babies, whose life is threatened because their immature lungs cannot provide adequate gas exchange. Another use is resuscitated drowning victims whose lungs are damaged and unable to supply adequate oxygenation without restorative healing. The extracorporeal circulation provides oxygenated blood to the lungs under the impetus of the patient's native heart and gives time to allow healing of the lungs to occur until the lungs can take over oxygenation. In excess of 1,000 ECMO procedures are conducted annually in the United States.
Another use of extracorporeal circulation is to provide heart support without supplementary oxygenation. For example, part of the blood flow bypasses the heart and instead passes through the extracorporeal circuit, thereby reducing a portion of the load on the heart.
While the applications and successes of extracorporeal circulation have been increasing, the need remains for limiting the duration of the extracorporeal circulation to a substantially as needed basis. The need exists for determining the as needed basis in terms of measuring patient performance during the extracorporeal circulation. A need exists for determining cardiac output during extracorporeal circulation. The need exist for determining cardiac output without requiring further intervention or cessation of treatment.